a) a negative electrode which intercalates with an alkali metal; b) a positive electrode comprising an electrode active material which intercalates with the alkali metal; c) a non-aqueous electrolyte activating the negative and the positive electrodes; and d) a phosphonate additive having the formula: (R1O)P(???O) (OR2) (R3) provided in the electrolyte, wherein R3 is a hydrogen atom and R1 and R2